Field of the Invention
This invention relates to agent dispensers of the fluid imbibing type, such as those which are driven osmotically and, more particularly, to an improvement for such an agent dispenser to render it suitable for continuous operation.
The invention is an improvement over agent dispensers described in U.S. Pat. Nos 3,760,984, 3,987,790, 3,995,631, 4,034,756, 4,474,575 and 4,539,004, all of which are incorporated herein by reference. In each of these patents, an agent dispenser is disclosed which is osmotically driven and whose size renders it suitable for use as a therapeutic system for administering agents to animals and humans. The dispenser includes an inner agent receiving means, such as a flexible bag that holds an agent to be dispensed, an intermediate fluid imbibing means such as a layer of an osmotically effective solute composition, for example, an inorganic salt, and an outer membrane that is permeable to fluid such as water and encapsulates both the bag and the solute layer. The bag has a discharge port which allows the agent to be directed to a location of use.
The agent dispenser is actuated by filling the bag with a flowable agent to be dispensed and by placing the dispenser in an environment, such a body cavity or a containment vessel. Fluid, typically water, is imbibed from the environment by the solute through the membrane and into the space between the inner bag and the membrane. The imbibed fluid squeezes the bag inwardly, thereby displacing the agent out of the discharge port.
A drawback in the use of all prior agent dispensers of the aforesaid type, particularly when used within a fluid containment vessel, is that the dispensers have been dependent upon either over-filling the containment vessel or maintaining the vessel and the dispenser in one operational attitude. Thus, as the driving fluid in the containment vessel becomes depleted, a portion of the outer surface of the membrane can be out of contact with the driving fluid for a particular attitude of the dispenser, thereby causing a change in the flow rate of the agent out of the internal bag. This change in operation of the agent dispenser cannot be tolerated in many instances, and a need exists for improving the agent dispenser such that it can compensate for changes in the attitude or operative position of the agent dispenser and containment vessel. The present invention satisfies this need.